Concomitant with the development of electronic apparatus at the system and subsystem level has been the growth and refinement of large-scale integrated circuit (LSI) technology. Through this technology improved semiconductor manufacturing techniques have permitted the fabrication of more and more circuit components in or on the same semiconductor chip or substrate, whereby the electronic functional complexity of the chip approaches a system or subsystem level, as distinguished from more basic functional electronic circuits, such as logic gates, amplifiers, etc.
A particularly beneficial application of LSI technology has been in the area of digital systems, e.g. computers, and through which the microprocessor industry was born. A typical LSI system or subsystem may comprise a plurality of circuit components, such as various logic elements, including gates, flip-flops, etc., integrated together on a single chip, by manufacturing processes including photo-fabrication, silicon processing, wafer testing, and packaging. Within the overall integrated circuit, a plurality of interconnection highways or signal transmission paths are provided for interconnecting the individual circuit elements to one another, and thereby obtain some prescribed electronic system or subsystem. Thus, the LSI-fabricated electronic system may be considered as being comprised essentially of two components--i) the individual circuit elements and (ii) the interconnection paths between the circuit elements.
In an effort to achieve efficient functional design and to increase packaging density various fabrication design approaches have been used. One approach which permits a more general application of an array of chip components to a plurality of specific needs involves the organization of a plurality of substantially identical circuit components, that may be termed standard cells or unit building blocks, which may have either a fixed or variable functional identity, so that the system designer can tailor a chip to a particular application by suitably designing a scheme for interconnecting the necessary building blocks available in the array.
Unfortunately, even with improvements in semiconductor manufacturing techniques and new semiconductor device structure (e.g. CMOS, SOS, etc.,) a major portion of an LSI chip may be occupied by the interconnection highways (e.g. diffusions, semiconductor overlays, metallizations); it is not uncommon for a typical LSI array to allow only fifteen to twenty percent of chip area for the cells themselves. Therefore, proper design and tailoring of the cells and system interconnection design are critical areas of chip design. This becomes especially important when considering that the time and expense required to complete the manufacture of an LSI system may be undesirably increased if defects occur during cell integration processing, resulting in the need to begin the manufacturing process anew.
Recent developments in integrated circuit fabrication techniques have produced a connection formation scheme through which a laser may be used to selectively interconnect signal pathways (e.g. aluminum metallizations) between blocks. An example of such a proposed scheme has been reported by P. W. Cook et al, in IBM Technical Disclosure Bulletin Vol. 17, No. 1, June 1974. In accordance with this reported fabrication technique, redundant blocks are connected to an interconnection highway comprised of signal and test tracks by directing pulsed laser light onto a metallization layer of aluminum, for example, in order to join the aluminum to underlying interconnection tracks diffused in the surface of a substrate. The diffused interconnection highways extend from the area of the aluminum metallization to clusters of redundant logic blocks or chips, each of which is identical to the others. Prior to interconnecting the blocks to the metallizations, the blocks may be tested by a separate testing highway path.
Another discussion of the use of pulsed laser energy to interconnect an aluminum metallization layer to an underlying diffused semiconductor region may be found in Vol. SC-10, No. 4, August 1975 of the Journal of Solid State Circuits, in an article by L. Kuhn et al, entitled "Experimental Study of Laser Formed Connections for LSI Water Personalization".
Now, although the above-described use of lasers to selectively join redundant blocks to interconnection highways may offer improved integration and a possible reduction in the number of package levels required for a complete LSI module, it does not take full advantage of the beneficial aspects of the unit cell approach to logic design and the manner in which it may be implemented by laser modification techniques, so as to permit a considerable savings in both the processing scheduling and expense involved in conventional LSI fabrication techniques.